1. Field of the Invention
The present invention concerns a data processing system comprising a plurality of data processing units that operate independent of each other.
2. Description of the Related Art
Examples of a data processing system, comprising a plurality of data processing units that operate independent of each other, include portable terminals, such as portable phones that are enabled to perform moving image communication.
With progresses in the furnishing of a high-speed communication infrastructure for third-generation mobile communication, etc. in recent years, the transmittable amount of information has increased significantly and moving image communication has become possible.
In accompaniment, the display functions of a portable terminal, such as a portable telephone, etc., are changing from those that are mainly for graphics display, such as the display of the time, menus, remaining battery quantity, etc. to those for moving image displays, such as synthesized images of moving images and graphics, etc.
Generally, an enormous amount of data is processed in the data processing of a moving image. Thus, when all processes, including moving image processes, are to be performed by a single data processing unit, such as a general-purpose processor, etc., the data processing unit is required to exhibit an extremely high performance.
Thus, in many cases, a data processing unit that satisfies the required performance either does not exist or the realization of a data processing unit that satisfies the required performance is difficult to attain.
Conventional portable terminals are thus equipped with a separate data processing unit or LSI (large scale integrated circuit) that is dedicated to moving image processing.
As prior-art examples, an arrangement of a display system of a portable terminal that performs only graphics display is shown in FIG. 6, and an arrangement of a display system of a portable terminal that is enabled to perform moving image communication is shown in FIG. 7.
Presently for moving image communication by a portable terminal, MPEG-4, which is an international standard for high-efficiency moving image coding, is most likely to be used.
In many cases, a MPEG-4 moving image data processing unit is equipped with on-screen display (OSD) functions for handling graphics, functions for synthesizing moving image data and graphics data, and functions for outputting image data to a display data processing unit.
Prior-art portable terminal display systems shall now be described with reference to FIGS. 6 and 7.
As shown in FIG. 6, a display system that performs only graphics display comprises, in outline, a CPU (central processing unit) 302, a display device 303, a voltage regulating device 311, and a clock generating device 312.
A CPU 302 generates graphics data to be displayed. The display device 303 displays the graphics data output from the CPU 302.
The voltage regulating device 311 supplies optimal power supply voltages from a system power supply 324 to the CPU 302 and display device 303. The clock generating device 312 supplies clocks to the CPU 302 and display device 303.
The CPU 302 operates by a power supply voltage 325, which is supplied from the voltage regulating device 311, and a clock 329, which is supplied from the clock generating device 312.
The display device 303 operates by a power supply voltage 328, which is supplied from the voltage regulating device 311, and a clock 332, which is supplied from the clock generating device 312.
The flow of the processes of the display system of FIG. 6 shall now be described.
The graphics data to be displayed by the display device 303 is output as output data 314 from the CPU 302 to the display device 303.
The graphics data that are output are graphics data concerning a menu display, time display, etc.
These graphics data are input directly as an external input 313.
Alternatively, these graphics data are stored inside the CPU 302 in advance and output to and displayed by the display device 303 in accordance with information input as the external input 313.
As shown in FIG. 7, a portable terminal display system that can perform moving image communication comprises, in outline, an image processing LSI 401, a display device 103, a CPU 102, a voltage regulating device 111, and a clock generating device 112.
The image processing LSI 401 has the functions of decoding coded data that have been coded in accordance with the MPEG-4 coding method and synthesizing the decoded moving image with graphics data.
The display device 103 displays the display image data generated by the image processing LSI 401.
The CPU 102 prepares graphics data to be displayed on the display device 103 and sends these data to the image processing LSI 401.
Also, when a moving image is to be displayed on the display device 103, the CPU 102 sends the coded data of the moving image to be displayed to the image processing LSI 401.
The voltage regulating device 111 supplies optimal power supply voltages from the system power supply 124 to the image processing LSI 401, CPU 102, and display device 103.
The clock generating device 112 supplies clocks to the image processing LSI 401, CPU 102, and display device 103.
The CPU 102 operates by a power supply voltage 125, which is supplied from the voltage regulating device 111, and a clock 129, which is supplied from clock generating device 112.
The image processing LSI 401 operates by a power supply voltage 426, which is supplied from the voltage regulating device 111, and a clock 430, which is supplied from the clock generating device 112.
The display device 103 operates by a power supply voltage 128, which is supplied from the voltage regulating device 111, and a clock 132, which is supplied from the clock generating device 112.
The flow of the processes of the display system of FIG. 7 shall now be described.
The CPU 102 outputs graphics data, concerning the time, menus, etc., as well as bit stream data, which are MPEG-4 coded data, to the image processing LSI 401 as output data 414.
The graphics data and the MPEG-4 coded data, which are moving image data, output to image processing LSI 401 are input into CPU 102 as an external input 113.
Alternatively, these data are stored in the interior of the CPU 102 in advance and output in accordance with information input from the external input 113.
At the image processing LSI 401, the MPEG-4 coded data are decoded and reconfigured as an image at the image processing unit 404.
The process of synthesizing the decoded image data and the graphics data input from the CPU 102 is then performed at the image processing unit 404.
The display data resulting from image synthesis are then output to display the device 103 as output data 418 of the image processing LSI 401.
The display device 103 performs screen display based on the display data.
However, in general, even with a portable terminal that is enabled to perform moving image communication, the displays will mainly be displays besides moving images, such as a time display, menu displays, etc.
In such cases, moving image data processing is not necessary and only graphics data are displayed.
Thus, with a prior-art data processing system having an arrangement such as that shown in FIG., 7, only graphics data will be output from the CPU 102.
In addition, at the image processing unit 404 inside the image processing LSI 401, the decoding of MPEG-4 coded data and the synthesizing of a decoded image with graphics data are not performed and the graphics data are output as they are as display data to the display device 103.
Although the realization of low power consumption is an important theme for battery-driven portable terminals, with the prior-art data processing system shown in FIG. 7, power and clocks are supplied to the MPEG-4 image processing parts (moving image decoding process part and synthesizing process part) inside the image processing unit 404 even when only graphics data are output.
There is thus the problem in that power is consumed wastefully in the form of unnecessary power consumption by the charging and discharging of a clock line and power consumption due to leak currents in the standby state.